In addition to being nutrients that are essential for growth of vertebrates, including humans, highly unsaturated fatty acids in recent years have been frequently reported to be involved in cardiovascular diseases and inflammatory diseases. There have been many reports of findings that the intake of n-3 type highly unsaturated fatty acids, such as docosahexaenoic acid and eicosapentaenoic acid, is particularly useful for human health. There have been reports that the ratio of intake amount of n-3 type highly unsaturated fatty acid to intake amount of n-6 type highly unsaturated fatty acid is important. Today's society is characterized in that there are trends for the increased ingestion of calories, cholesterol, and n-6 type highly unsaturated fatty acids, and there is a trend for decreased ingestion of n-3 type highly unsaturated fatty acids. These trends have come to be considered to be related to various types of adult-onset diseases or the like.
Fish oil is an oil that is rich in n-3 type highly unsaturated fatty acids. The intake of such fish oil is widely recommended, and methods are being devised for the concentration of the n-3 type highly unsaturated fatty acids in fish oil for more efficient intake of n-3 type highly unsaturated fatty acids. The concentration of highly unsaturated fatty acids using lipase reactions is one such method.
Lipases are enzymes that catalyze hydrolysis reactions to decompose oils into free fatty acids and glycerin. Various types of animals and plants and microorganisms are known to have lipases. A kind of the lipases does not necessarily have the same effect on all fatty acids. Differences in the activity of lipases occur due to bonding position within the glyceride, carbon chain length of the fatty acid, number of double bonds, or the like. It is thus possible to selectively hydrolyze fatty acids using such lipases, and as a result, it becomes possible to concentrate a specific fatty acid within the glyceride fraction. For example, when a lipase produced by a kind of the genus Candida is used, it is known that hydrolysis reaction of fish oil results in concentration of highly unsaturated fatty acids, such as docosahexaenoic acid, in the undecomposed glyceride fraction (Patent Document 1).
Hydrolysis reaction by lipase in this manner is a method that is effective for the concentration of highly unsaturated fatty acids. The concentration of highly unsaturated fatty acid in the glyceride fraction increases with progress of hydrolysis with respect to fatty acids other than those of the target highly unsaturated fatty acid.
Although attention is paid to the ingestion of oils just like the ingestion of triglycerides, the cholesterol content is also important. The excessive ingestion of cholesterol is thought to result in the ready occurrence of arterial sclerosis and cardiac infarction, and thus such excessive ingestion is thought to be undesirable. In addition to triglycerides, the raw fish oils and microbial oils that contain highly unsaturated fatty acids also include cholesterol.
In Patent Document 2, a method for adding a volatile working fluid and for use of distillation for removal of the free form of cholesterol from an oil containing highly unsaturated fatty acid is described.